The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A typical multi-speed automatic transmission uses a combination of torque transmitting devices, such as clutches, dog clutches/synchronizers, or brakes, to achieve a plurality of forward and reverse gear or speed ratios as well as a Neutral and a Park. Selection of speed ratios is typically accomplished by a microprocessor transmission control module that employs various vehicle parameters, for example vehicle speed, and various driver input signals, for example accelerator pedal position, to select the appropriate speed ratios. The transmission then engages a combination of the toque transmitting devices to provide the desired speed ratios.
In order to engage the torque transmitting devices, a typical automatic transmission includes a hydraulic clutch control system that employs a hydraulic fluid to selectively actuate pistons within the torque transmitting devices. Actuation of a piston in turn engages the torque transmitting elements within the torque transmitting device. One piston design, known as a dual-area piston, includes two areas located on the piston that are hydraulically isolated from one another. One area is pressurized by the hydraulic fluid from the hydraulic clutch control system in order to stroke the piston. The non-pressurized area is typically connected to an exhaust backfill circuit to help prevent the creation of a vacuum within the non-pressurized area as the piston strokes. However, if the exhaust backfill circuit is unable to adequately provide a fluid to fill the non-pressurized area, issues with fluid pressure control and air entrainment may arise. Accordingly, there is a need in the art for a multi-area clutch assembly that is designed to minimize the creation of a vacuum in the non-pressurized area to thereby improve pressure control and prevent air entrainment, and that is also inexpensive and automatic.